We have measured the ratio (gi) /F(gi) over the range 0.029 ( x ( 0.8 and 1.3 (Q+/- ( 10 (GeV/c) using deep-inelastic scattering of polarized electrons from polarized ammonia. An evaluation of the integral fo g+/_ (x, Q2) dx at fixed Q2 = 3 (GeV/c)2 yields 0.127 +/- 0.004(stat) +/- 0.010(syst), in agreement
with previous experiments, but well below the Ellis-Jaffe sum rule prediction of 0.160 +/- 0.006. In the
quark-parton model, this implies Aq = 0.27 +/- 0.10.This work was supported by Department of Energy Contracts No. DE-AC05-84ER40150 (CEBAF), No. W-2795-Eng-48 (LLNL), No. DE-AC0376SF00515 (SLAC), No. DE-FG03-88ER40439 (Stanford), No. DE-FG05-88ER40390 and No. DEFG05-86ER4026 (Virginia), and No. DE-AC02-76ER00881 (Wisconsin); by National Science Foundation Grants No. 9114958 (American), No. 9307710 (Massachusetts), No. 9217979 (Michigan), No. 9104975 (ODU) and No. 9118137 (U. Penn.); by the Schweizersche Nationalfonds (Basel); by the Commonwealth of Virginia (Virginia); by the Centre NAtional de la Recherche Scientifique and the Commissariat a l'Energie Atomique (French groups); and by the Japanese Ministry of Education, Science and Culture (Tohoku)
